Art of cracking



March 16, 1937. E. c HER 2,073,934

! ART OF CRACKING Filed June 16, 1933 INVENTOR Eager/e C flerf/ns/ ATTORNEYS Patented Mar. 16, 1937 UNITED STATES PATENT OFFIE Sinclair Refining Company,

New York, N. Y.,

S a corporation of Maine Application June 16, 1933, Serial No. 676,057

6 Claims.

This invention relates to improvements in the manufacture of gasoline, by cracking, which accomplish, particularly in combined operations involving the production or handling of high boiling residual stocks, extreme concentration of liquid residues without involving the degradation of such residues usually encountered when they are concentrated to an equivalent extent.

Combined operations. in which reduced crude 10 oil, or some equivalent residual stock, or the hot oil'products of another cracking operation are discharged into a common vapor separator with the hot oil products of a cracking operation to which stock of high boiling gas oil charl5 acter, usually consisting of or including a fraction of that character produced in the operation, is supplied have been proposed and practiced for some time past in the manufacture of gasoline. In such operations the residual com- 20130116 11178 of all of the several mixtures entering the vapor separator are discharged therefrom as a composite tar. The hot oil products of an operation in which stock of high boiling gas oil character is cracked, particularly when that stock 33 includes recycled stock, however, include substantial amounts of oil constituents of boiling range abutting that of the composite tar separated in the common vapor separator, and the presence of these constituents, in substantial amounts, tends 0 to repress the separation of constituents of similar character as vapors from the residual tar separated therein. As a consequence, the composite tar usually includes substantial amounts of oil constituents which would be more appropri- 35 ate as components of a distillate fraction. The production of residual tar, normally the least valuable product of the combined operation, is thus increased while the production of the more valuable distilled fractions, free from tar constituents, is decreased. The usual result of attempts to increase the proportion of such oil constituents separated from the tar by increasing the temperature in the vapor separator is a degradation, though decomposition, of the remaining tar offsetting any advantage that may be attained through increased recovery of distillate fractions.

This invention provides a combined operation in which the functions of the conventional comrnon vapor separator are divided between two vapor separators in a special manner to accom- 1 plish extreme tar concentration without tar degradation, in effect to add a new function to I those of the common vapor separator. 55 According to the present invention, a stream of high boiling oil, of high boiling gas oil character for example, is forced through a heater and heated therein to a high cracking temperature, upwards of 900 F. for example, and the hot oil products from this heater are discharged into a first vapor separator, an independent stream of lower boiling range, of low boiling gas oil character or lower boi1ing or even of gasoline character for example, is forced through a separate heater and heated therein to a high cracking temperature and the hot oil products from this heater are discharged into a separator, a second vapor separator, the vapor mixtures escaping from both vapor separators are combined and subjected, as a composite mixture, to a common fractionating operation from which a low boiling fraction including the gasoline product is taken off and condensed, a higher boiling fraction separated in the fractionating operation is supplied to the first-mentioned heating operation, a residual oil to be concentrated to a maximum, reduced crude oil or a cracked tar for example, including oil constituents corresponding to components of the high boiling oil supplied to the first-mentioned heating operation is introduced into the second vapor separator, an oil of boiling range lower than that of this residual oil, of gas 011 character for example, is introduced into the first vapor separator to assist in controlling the temperature therein, the residual oil introduced into the second vapor separator similarly assisting in controlling the temperature therein, and tar is discharged from both vapor separators. The tar constituents introduced into the first vapor separator are, principally if not exclusively, the tar constituents produced in the cracking of the high boiling oil in the firstmentioned heating operation, but the tar, or residual, constituents introduced into the second vapor separator include those of the introduced residual stock. In the second vapor separator, however, oil constituents of boiling range abutting that of the tar separated therein are present, if at all, in but minor amounts so that, instead of being repressed, the separation of such constituents as vapors from the residual tar separated therein is promyoted by the so-called partial pressure effect of the hot oil products discharged from the second-mentioned heating operation. Thus, in the second vapor separator, a more complete separation as vapors of such oil constituents is effected than would be expected from the prevailing temperature whereas, in the conventional common vapor separator, a less complete separation as vapors of such oil constituents is effected than would be expected from the prevailing temperature. The temperature in both separators in carrying out the combined operation of this invention, moreover, is controlled to avoid degradation of the separated residues. The high boiling oil supplied to the first-mentioned heating operation may consist exclusively of or may comprise a fraction separated in the fractionating operation to which the vapors escaping from both vapor separators are subjected, the constituents suitable as components of this stock separated as vapors in the second vapor separator from a stock such as reduced crude oil or cracked tar introduced into the second vapor separator being thus delivered to the first-mentioned heating operation. The oil of lower boiling range supplied to the secondmentioned heating operation may consist exclusively of or may comprise a fraction of lower boiling range, that is of intermediate boiling range, separated in the same fractionating operation. The stock supplied to the first-mentioned heating operation may have, with advantage, a.

boiling range approximating 500750 F. and that supplied to the second-mentioned heating operation may have, with advantage, a boiling range approximating 400-600 F., for example.

It will be apparent that the invention is capable of embodiment in combined operations of widely varying type. For example, the second-mentioned heating operation may be carried out for cracking a Wide variety of stocks of boiling range lower than that of the high boiling gas oil character stock supplied to the first-mentioned heating operation, for cracking stocks higher boiling than gasoline or for reoracking cracked gasoline or cracking straight-run gasoline to improve the anti-knock value of such gasoline. Again for example, a wide variety of residual stocks and of mixtures of such stocks can be subjected to concentration in the second vapor separator, including crude oil, and reduced crude oil and cracked tars from. other operations of widely varying type. In one embodiment of the r invention, the residual tar discharged from the first vapor separator is introduced into the second vapor separator to be concentrated therein. This operation involves the introduction into the second vapor separator of higher boiling oil constituents typically produced by the cracking of stocks of high boiling gas oil character, but only in the proportion in which they are present in the tar discharged from the first vapor separator, not in the proportion in which they are introduced into the first vapor separator from the firstmentioned heating operation. An improved concentration of the tar constituents produced in the cracking of the oil of lower boiling range in the second-mentioned heating operation, in the second vapor separator, is also characteristic of the invention.

The invention will be further described in connection with the accompanying drawing which illustrates, diagrammatically and conventionally, in elevation and partly in section and with parts broken away, one form of apparatus adapted for the practice of the invention.

In carrying out the combined operation of the invention in the apparatus illustrated, the residual oil to be concentrated to a maximum is introduced into the vapor separator 2, the hot oil products from the heater to which the lower boiling of the stocks to be cracked is supplied being introduced into this vapor separator and the hot oil products from the heater to which the higher boiling of the stocks to be cracked is supplied being introduced into vapor separator I. The higher boiling of the stocks to be cracked, a stock of high boiling gas oil charact-er for example, is forced, by means of pump 3 through connection 4, through heater 5 and thence, through connection 6 including pressure reducing valve I, into vapor separator I. Tar constituents separated in vapor separator I are discharged as a liquid through connection 8. The temperature within vapor separator I is controlled by the reflux condenser-heat exchanger 9 assisted by the regulated introduction, through valved connections II] and II, of, for example, a stock of gas oil character, supplied through connection I2 by means of pump I3. The temperature in the lower part of vapor separator I may be maintained, for example, in the neighborhood of 740-760 F. The vapor mixture escaping from vapor separator I passes, through connections I4 and I5, into the fractionating tower 16, together with the vapor mixture escaping from vapor separator 2 which passes, through connections I! and I5, into fractionating tower I6. A high boiling fraction, including the highest boiling constituents entering the tower, is separated in fractionating tower I6 and discharged through connection I8 to pump 3 to be supplied to the heater 5. This fraction includes the constituents falling within its boiling range separated as vapors in both vapor separator I and vapor separator 2 and any additional constituents of this boiling range introduced directly into tower I6 through connections I2 and E9. Stock to be supplied to a heater 5 may thus consist of or comprise a high boiling distillate fraction separated as vapors from the residual stock, reduced crude oil or a cracked tar for example, introduced into vapor separator 2, or a, high boiling distillate fraction separated from a raw stock, gas oil for example, introduced into vapor separator I, or a raw stock introduced directly to fractionating tower I5, or a mixture of such stocks, in admixture with those constituents of the hot oil products discharged from heater 5 and heater 2!) of this boiling range. A low boiling fraction including the gasoline product is taken ofr", through connection 2|, from fractionating tower I6 and condensed in condenser 22. The condensate, separated in receiver 23 from uncondensed vapors and gases, is discharged through connection 24, uncondensed vapors and gases being discharged through connection 25. The fractionation eifected in fractionating tower I6 is controlled by a reflux condenser-heat exchanger 26 assisted by the regulated introduction, through connection 21 by means of pump 28, of a part of the condensate collected in receiver 23. A fraction of intermediate boiling range may be separated in fractionating tower I6 and discharged, as a side stream, through connection 29 and either or both of valved branch connections 30 and 3|.

The lower boiling of the stocks to be cracked is forced, by means of pump 32, through reflux condenser-heat exchanger 33 and connection 34, through heater 20 and thence, through connection 35 including pressure reducing valve 36, into vapor separator 2. The residual stock to be concentrated to a maximum is introduced, through connection 37, into vapor separator 2. The tar constituents separated in vapor separator 2 are discharged as a liquid through connection 38. The tar constituents separated in vapor separator I are, principally if not exclu- ,sively, the tar constituents produced in the cracking of the stock supplied to heater 5, but the tar constituents separated in the vapor separator 2 include the tar constituents of the residual stock or stock mixture introduced through connection 31 as well as those produced in the cracking of the stock supplied to the heater 2%). The temperature in vapor separator 2 is controlled by reflux condenser-heat exchanger 35 assisted by the regulated introduction of residual stock through connection 31. The temperature in the lower part of vapor separator 2 may be maintained, for example, in the neighborhood of 750-765 F. The stock supplied to heater 263 may consist of an intermediate fraction separated in fractionating tower I6, supplied through connections 29 and 39, or of a stock of similar character of boiling range lower than that of the stock supplied to heater 5, supplied through connection 45, or a gasoline character fraction, supplied through connection 45, or a mixture of such stocks.

The cooling medium circulated through the reflux condensers-heat exchangers I4 and 25 may consist, with advantage, of crude oil thus to be preheated in connection with a topping operation. For example, crude, oil, supplied by means of pump 4| through connection 42, may be passed successively through reflux condenser-heat exchanger 25 and reflux condenser-heat exchanger I4 and thence introduced, through connection 43, into a combined vapor separator and fractionating tower 44 for separation of fractions vaporized by the heat absorbed in these reflux condensers-heat exchangers. Assuming the crude oil to be heated to a temperature of 500-600 F., in these reflux condensers-heat exchangers, for example, a gasoline fraction and one or two intermediate fractions of kerosene character, or low boiling gas oil character. may be recovered as distillate fractions from the tower 44, being discharged, respectively, through connections 45, 46, and 4'! to condensers and coolers not shown. Connection 48 is provided for the introduction of a refluxing medium to assist in controlling the operation of the tower. The thus reduced crude is discharged through connection d9. If this reduced crude is the residual stock to be concentrated to a maximum, it is forced, by means of pump 50 through connection 5|, through heater 52, heated therein to a temperature shortof that at which any objectionable decomposition occurs during the time within which it is in the heater, '750-800 F. for example, and discharged, through connections 53 and 31, into the vapor separator 2. 'The gasoline fraction or the kerosene fraction or fractions separated in fractionating tower G4, or mixtures of them, may be supplied to heater 28 through connection 40, alone or in admixture with other stocks such as an intermediate fraction separated in fractionating tower It. If a gas oil fraction is separated in fractionating tower 44, it may be supplied to vapor separator l or fractionating tower it through connection I2. If the cracked tar separated in vapor separator l is the residual stock to be concentrated to a maximum, it is introduced, by means of pump 54 through connections 55 and 31, into vapor separator 2. Mixtures of stocks such as reduced crude oil and cracked tars including tars from other cracking operations as well as tar from vapor separator I may be introduced into vapor separator 2 through connection 31 to be concentrated therein.

The precise characters of the cracking operations carried out in the heater 5 and in the heater 25 are not essential to the invention, it being important only, in carrying out the invention in apparatus such as that illustrated, that the stock supplied to heater 2% be of lower boiling range than that supplied to heater 5 and that the stocks supplied to both heaters be heated to relatively high cracking temperatures therein. In the heater 5, for example, the stock supplied thereto may be heated to a temperature of 940965 F. under a pressure of 200-600 pounds per square inch as discharged therefrom, and in the heater 25, for example, the stock supplied thereto may be heated to a temperature of 970-985 F. under a pressure of 300-600 pounds per square inch as discharged therefrom. In vapor separator I as well as vapor separator 23, concentration of the separated liquid residues is promoted by the maintenance of lower rather than higher pressures; in general the pressure in the vapor separators may be maintained in the neighborhood of 10-50 pounds per square inch. To minimize degradation of the separated liquid residues, it is advantageous to maintain a minimum volume of separated liquid within the vapor separator, and to assist in the maintenance of such minimum liquid volume while maintaining liquid discharge, through connections 8 and 38 in the apparatus illustrated, it is advantageous to provide tar legs of reduced cross section as shown at 56 and 5?.

The invention makes possible a reduction of the total tar make of as much as 50% or more comparing an operation embodying the division of the functions of the conventional common va- 'por separator in accordance with the invention with an operation using the conventional common vapor separator.

I claim:

1. In the manufacture of gasoline, the improvement which comprises forcing a stream of high boiling oil through a heater and heating it therein to a high cracking temperature and discharging the hot oil products into a vapor separator, forcing an independent stream of oil of lower boiling range through a separate heater and heating it therein to a high cracking temperature and discharging the hot oil products into a separate vapor separator, combining the vapor mixtures escaping from both vapor separators and subjecting the composite mixture to a common fractionating operation and taking off from this fractionating operation and condensing a low boiling fraction including the gasoline product, supplying a higher boiling fraction separated in this fractionating operation to the first-men-- tioned heating operation, introducing a relatively cool residual oil including constituents corresponding to components of the high boiling oil supplied to the first-mentioned heating operation into the second-mentioned vapor separator, introducing a relatively cool oil of lower boiling range into the first-mentioned vapor separator, and discharging tar from both vapor separators.

2. In the manufacture of gasoline, the improvement which comprises forcing a stream of high boiling oil through a heater and heating it therein to a high cracking temperature and discharging the hot oil products into a vapor separator, forcing an independent stream of oil of lower boiling range through a separate heater and heating it therein to a high cracking temperature and discharging the hot oil products into a separate vapor separator, combining the vapor mixtures escaping from both vapor separators and subjecting the composite mixture to a common fractionating operation and taking oif from this fractionating operation and condensing a low boiling fraction including the gasoline product, supplying a higher boiling fraction separated in this fractionating operation to the first-mentioned heating operation, supplying a fraction of intermediate boiling range separated in this fractionating operation to the second-mentioned heating operation, introducing a residual oil including constituents corresponding to compo nents of the high boiling oil supplied to the firstmentioned heating operation into the secondmentioned vapor separator, introducing an oil of lower boiling range into the first-mentioned vapor separator, and discharging tar from both vapor separators.

3. In the manufacture of gasoline, the improvement which comprises forcing a stream of high boiling oil through a heater and heating it therein to a high cracking temperature and discharging the hot oil products into a vapor separator, forcing an independent stream of oil of lower boiling range through a separate heater and heating it therein to a high cracking temperature and discharging the hot oil products into a separate vapor separator, combining the vapor mixtures escaping from both vapor separators and subjecting the composite mixture to a common fractionating operation and taking off from this fractionating operation and condensing a low boiling fraction including the gasoline product, supplying a higher boiling fraction separated in this fractionating operation to the firstmentioned heating operation, introducing relatively cool reduced crude oil into the secondmentioned vapor separator, introducing a relatively cool oil of lower boiling range into the firstmentioned vapor separator, and discharging tar from both vapor separators.

4. In the manufacture of gasoline, the improvement which comprises forcing a stream of high boiling oil through a heater and heating it therein to a high cracking temperature and discharging the hot oil products into a vapor separator, forcing an independent stream of oil of lower boiling range through a separate heater and heating it therein to a high cracking temperature and discharging the hot oil products into a separate vapor separator, combining the vapor mixtures escaping from both vapor separators and subjecting the composite mixture to a common fractionating operation and taking on from this fractionating operation and condensing a low boiling fraction including the gasoline product, supplying a higher boiling fraction separated in this fractionating operation to the firstmentioned heating operation, introducing relatively cool reduced crude oil into the secondmentioned vapor separator and relatively cool gas oil into the first-mentioned vapor separator, and discharging tar from both vapor separators.

5. In the manufacture of gasoline, the improvement which comprises forcing a stream of high boiling oil through a heater and heating it therein to a high cracking temperature and discharging the hot oil products into a vapor separator, forcing an independent stream of oil of lower boiling range through a separate heater and. heating it therein to a high cracking temperature and discharging the hot oil products into a separate vapor separator, combining the vapor mixtures escaping from both vapor separators and subjecting the composite mixture to a common fractionating operation and taking off from this fractionating operation and condensing a low boiling fraction including the gasoline product, supplying a higher boiling fraction separated in this fractionating operation to the firstmentioned heating operation, introducing tar from the first-mentioned vapor separator into the second-mentioned vapor separator, introducing a relatively cool oil of lower boiling range into the first-mentioned vapor separator, and discharging tar from the second-mentioned vapor separator.

6. In the manufacture of gasoline, the improvement which comprises forcing a stream of oil of boiling range approximating 500-'750 F. through a heater and heating it therein to a high cracking temperature and discharging the hot oil products into a vapor separator, forcing an independent stream of oil of boiling range approximating 400600 F. through a separate heater and heating it therein to a high cracking temperature and discharging the hot oil products into a separate vapor separator, combining the vapor mixtures escaping from both vapor separators and subjecting the composite mixture to a common fractionating operation and taking off from this fractionating operation and condensing a low boiling fraction including the gasoline product, supplyinga higher boiling fraction separated in this fractionating operation to the first-mentioned heating operation, introducing a relatively cool residual oil including constituents corresponding to components of the high boiling oil supplied to the first-mentioned heating operation into the second-mentioned vapor separator, introducing a relatively cool oil of lower boiling range into the first-mentioned vapor separator, and discharging tar from both vapor separators.

EUGENE C. HERTHEL. 

